In the manufacture of absorbent articles, structures with high void volume are desired for high absorbent capacity. However, the large pore size of high bulk structures typically provides relatively low capillary pressure for wicking of the fluid. Further, high bulk structures require substantial space, leading to high costs for shipping, storage, and packaging. Ideally, an absorbent article would be relatively flat and dense prior to use and would expand when wetted to provide needed pore space. Prior art structures that can expand when wetted, such as air-laid webs of crosslinked fibers or wet-laid noncompressively dried wet resilient tissues tend to be relatively isotropic in wicking fluids, meaning that the spread of menses, urine, or other fluids tends to be relatively circular about the region of fluid entry. Isotropic wicking is generally not desired because for most absorbent articles have a dominant longitudinal direction. For best utilization of the full absorbent article, it is preferred that wicking be predominantly in the longitudinal direction. Past efforts to increase longitudinal fluid flow have met limited success. These methods include embossing or densification of longitudinal zones to promote longitudinal wicking. It is desired that an absorbent article provide enhanced longitudinal wicking in addition to also expanding when wetted to provide more void volume. Ideally, an absorbent structure should be heterogeneous in terms of effective pore size such that large pores and small pores are available for effective wicking, while having a preferred longitudinal direction. Further, it is desired that the components of the absorbent article be inexpensive, such as a tissue web which can be produced with conventional tissue making.
A further widespread deficiency in prior absorbent articles such as diapers, feminine pads, incontinence pads, and other absorbent garments is the inability to maintain a close-to-body fit in use when the article has been wetted by body fluids. An article that fits well when dry generally sags, collapses, or otherwise descends from the body when it is wetted, especially if the added fluid contributes a significant amount of mass to the article, as often occurs during urine discharge. Feminine pads are especially difficult to maintain close to the body, given the complex contours of feminine anatomy and the high deformation and stress imposed on the article by normal body motion. The decrease in bulk and elastic modulus that occurs as cellulose fibers are wetted also contributes to the inability of typical feminine pads to maintain excellent fit against the wearer's body. Improved close-to-body fit in a wide variety of absorbent articles is needed, but has heretofore been impractical or highly difficult to achieve. Contoured, resilient, absorbent articles can be postulated using known materials if cost is not a factor, but the challenge is inventing high-quality absorbent articles that are also suitably inexpensive for one-time use. Ideally, such high-performance articles could be mass produced with existing equipment and with inexpensive materials.
Therefore, there is a need for a material which realizes the previously incompatible objectives for absorbent articles of low cost and excellent close-to-body fit even when wetted by body fluids, while also providing additional noteworthy and novel advantages such as improved absorbent capacity, reduced dry thickness, improved fluid handling and controlled directionality of fluid transport.